Abstract
Evidence regarding the relationship between dietary or supplemental vitamin C intake and human papillomavirus infection is limited. Therefore, this study aimed to evaluate if dietary and/or supplemental vitamin C intake is independently associated with human papillomavirus (HPV) infection and compare them. The analysis utilized data extracted from the National Health and Nutrition Examination Survey spanning from 2007 to 2016. The study cohort comprised 950 women within the age range of 18 to 59 years. The associations between dietary and supplemental vitamin C intake and cervicovaginal human papillomavirus infection were estimated using weighted logistic regression, interaction analyses, and subgroup analyses based on complex multistage sampling. Adjusted binary logistic regression revealed that supplemental vitamin C intake was negatively associated with the risk of HPV (adjusted odds ratio [AOR] 0.94, 95% confidence interval [CI] 0.89–0.99) and high-risk human papillomavirus infection (AOR = 0.76, 95% CI = 0.55–0.99). However, we did not find an association between dietary vitamin C and human papillomavirus infection (AOR = 1.18, CI = 0.96–1.45). Subgroup analyses indicated that supplemental vitamin C was only negatively associated with human papillomavirus infection in women older than 25 years (P = .03) and was more strongly associated with HPV infection in those who did not receive HPV vaccination (Pinteraction = 0.03). The results from a nationally representative sample from the United States supported that the protective effect of vitamin C against human papillomavirus infection was driven mainly by supplemental vitamin C rather than dietary vitamin C.
Keywords: HPV, NHANES, vitamin C
1. Introduction
The human papillomavirus (HPV) continues to be a substantial global health concern affecting women. The infection of HPV, especially strains 16 and 18, has been recognized as a contributing cause for almost all cervical cancers[1] and more than 5% of all cancers worldwide.[2] Nowadays, cervical cancer has become the fourth most prevalent cancer among women, considering both its incidence and mortality.[3] HPV vaccines came out in 2006 and have been included in the national vaccination programs of over 150 countries by 2021.[4] Approximately 90% of cervical cancers and HPV-linked illnesses are averted by the 9-valent HPV vaccine, though it does not offer complete protection.[5,6] Therefore, the detection of other variables that aid in avoiding HPV infections and cervical cancer development is essential.
Emerging evidence has indicated that vitamin C (VitC) or ascorbic acid intake may help prevent HPV infection, playing important roles in prevention, reduction in duration, and alleviation, during diverse infections.[7] VitC is an essential nutrient for humans that is required and involved in several physiological processes.[8,9] However, humans lack the ability to synthesize VitC and must obtain it through diet or supplements.[10] Previous studies have also investigated relationships between dietary VitC intake and HPV infection. A case-control study revealed a correlation between dietary VitC intake and a reduced risk of HPV persistence.[11] Barchitta et al reported that in women with insufficient VitC in the diet were at a higher risk of HPV infection in a univariable analysis[12] and another study by revealed the similar results for plasma levels of VitC.[13] Interestingly, a recent cross-sectional study indicated a U-pattern linkage between the concentration of VitC in serum and the incidence of HPV, with the minimal risk at plasma VitC level of approximately 69 μmol/L.[14] The VitC concentration showed a negative correlation with HPV infection, but only in patients from 25 to 59 years.[14]
In humans, VitC can be consumed in the diet or as synthetic supplements. Although both natural and synthetic VitC are chemically and biologically identical,[10] the relationships between dietary VitC or supplemental VitC and HPV infection may differ. However, research has yet to investigate the correlations between dietary or supplemental intake of VitC and HPV infection separately. So we do not know which one of VitC or both has influence on HPV infection. Consequently, the purpose of this research was to explore the associations of both sources of VitC with the prevalence of cervicovaginal HPV infection. It will be more instructive for the intake of VitC to prevent HPV infection.
2. Methods
2.1. Data sources
Study data were sourced from the U.S. National Health and Nutrition Examination Survey (NHANES), a publicly accessible series of population-based investigations within the United States. The original study protocol can be accessed on the website of the Ethics Review Board of the National Center for Health Statistics (https://www.cdc.gov/nchs/nhanes/about/erb.html) and had received ethical clearance from the Ethical Review Committee (Protocols #98-12 and #2005-06). Each participant provide their written informed consent. This study is an analysis of publicly available anonymized data from the official NHANES website (https://www.cdc.gov/nchs/nhanes/). Thus, ethical review from the institutional review board is not needed.
2.2. Study population
This study, which was cross-sectional in nature, focused on women aged 18 to 59 who underwent HPV testing in the NHANES from 2007 to 2016. Responses in the NHANES data that were labeled as “inadequate,” “refused,” “don’t know,” or ‘missing’ were considered missing. Participants missing data on HPV, covariates, or dietary and supplemental VitC data were excluded. A total of 950 participants, including 389 in the HPV infection group and 561 in the no HPV infection group, were included in the current study. Details regarding the selected sample are provided in the flowchart (Fig. 1).
Figure 1.
Flowchart of patient selection, NHANES 2007–2016. NHANES = National Health and Nutrition Examination Survey, PIR = poverty income ratio.
2.3. Measurement and classification of variables
The public dietary data were sourced from the Centers for Disease Control and Prevention. VitC data were recorded as a continuous variable. Two 24-hour dietary recalls on separate days from the participants were collected by the automated multiple-pass method, a computer-based dietary interview program.[15–17] The acquisition and measurement of VitC from food and supplements are available within the NHANES database (https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/DR1IFF_E.htm).
The presence of HPV infection was ascertained through DNA genotyping from vaginal swab samples, utilizing the Digene hybridization capture method, prototype line blot assay, and Roche Linear Array in NHANES. We used the further information on NHANES laboratory methodology for HPV measurements, which is available on the website (https://wwwn.cdc.gov/Nchs/Data/Nhanes/Public/2007/DataFiles/HPVSWR_E.htm). High-risk HPV infection was classified as a dichotomous variable according to a positive test for at least one of HPV type 16 or 18.
The study evaluated variables such as age, race/ethnicity, educational background, poverty income ratio (PIR),[18] smoking status, age at first sexual intercourse, and the intakes of folate, nicotinic acid, and vitamins B1, B2, B6, B12, and D as variables. The age variable was continuous, covering the range from 18 to 59 years. The race/ethnicity of participants was self-reported and categorized into 5 groups: Mexican American, non-Hispanic White, non-Hispanic Black, other Hispanics, and other races. Levels of education were divided into high school graduate or below, some college, or college graduate or above. PIR was divided into low (below 1.3), middle (ranging 1.3–3.5), and high groups (above 3.5). In the questionnaire, smokers were identified as those smoked over 100 cigarettes. Participants’ count of sexual partners referred to the number of males they engaged in any sex throughout their lifetime.
2.4. Statistical analysis
Continuous variables are depicted as average values with standard errors, whereas categorical variables are represented as percentages. Baseline characteristics were evaluated using means, standard errors, percentages, or frequencies. For continuous variables, analysis of variance was used for those with a normally distribution, while nonparametric tests were applied for those nonnormally distributed variables. The analysis of categorical variables was conducted using the chi-square test.
Three models were constructed using multivariate binary logistic regression: Model 1, with no covariates adjusted; Model 2, with only sociodemographic data adjusted; and Model 3, with adjustments to sociodemographic data and other important nutrient intakes. To address the unequal probability of selection and nonresponse, we utilized the examination sampling weights from the Medical Examination Center. These sampling weights were used to adjust all estimates shown except when demographic characteristics were used to report the sample size. Odds ratios and 95% confidence intervals (CIs) between HPV infection (yes or no) and dietary/supplement VitC levels were estimated via weighted logistic regression.
To determine if the independent variable was divided into intervals, we employed smooth curve fitting. We applied segmented regression, which fits each interval with a distinct line segment. A log-likelihood ratio test was employed to assess whether a threshold existed by comparing a one-line (nonsegmented) model to a segmented regression model. The inflection point that connecting the segments was based on the model gives maximum likelihood, and it was determined using 2 steps recursive method. We performed sensitivity analyses by including or excluding other important nutrients for both the overall HPV group and the high-risk HPV group. The P values were modified with Bonferroni corrections to handle multiple comparisons. Stratified and interaction analyses were performed according to age and vaccination status. We used a weighting approach to reduce the significant volatility of our dataset.[19]
Data were analyzed using R version 4.1.2 (http://www.R-project.org, The R Foundation) and EmpowerStats version 4.0 (https://www.empowerstats.net/en/, X&Y Solutions, Inc., Boston, MA) software. Statistical significance was set at P < .05.
3. Results
The study comprised 950 participants after screening according to the inclusion and exclusion criteria. The participants were categorized into an HPV infection group (n = 389) and a no HPV infection group (n = 561). The sample represented 9, 817, 548 women in America according to a weighted sampling survey, with 6, 251, 754 participants with no HPV infection and 3, 375, 535 participants with HPV infection. Table 1 displays the weighted baseline characteristics of the chosen women based on their HPV infection status. Compared to those without HPV infection, those with HPV infection were younger and less likely to have a race of non-Hispanic White. HPV-infected women were more smokers and had a lower education level and PIR. In addition, women with HPV infected had more sexual partners and a younger age at first sexual intercourse. Women with a higher intake of supplemental VitC were less likely to have HPV infection (P = .003).
Table 1.
Weighted baseline characteristics of HPV infection and no HPV infection groups, NHANES 2007–2016.
| Clinical characteristics | HPV infection (n = 389, %) | No HPV infection (n = 561, %) | P * |
|---|---|---|---|
| Age, year, mean | 40.2 (11.8) | 42.7 (11.0) | .001 |
| Race/ethnicity | <.001 | ||
| Mexican American | 41 (6.0) | 60 (5.4) | |
| Other Hispanic | 41 (7.3) | 49 (4.0) | |
| Non-Hispanic White | 168 (64.1) | 317 (78.8) | |
| Non-Hispanic Black | 97 (15.2) | 65 (5.1) | |
| Other races | 42 (7.4) | 70 (6.7) | |
| Education | <.001 | ||
| High school graduate or less | 132 (28.0) | 156 (24.0) | |
| Some college | 145 (34.9) | 159 (26.5) | |
| College graduates or above | 112 (37.1) | 246 (49.5) | |
| PIR | .004 | ||
| <1.3 | 134 (22.8) | 134 (14.3) | |
| 1.3–3.5 | 122 (29.9) | 186 (32.2) | |
| >3.5 | 133 (47.3) | 241 (53.5) | |
| HPV vaccine | <.001 | ||
| No | 43 (12.7) | 31 (4.5) | |
| Yes | 346 (87.3) | 530 (95.5) | |
| Smoke | .022 | ||
| No | 169 (45.9) | 188 (38.2) | |
| Yes | 220 (54.1) | 373 (61.8) | |
| Sex partners | <.001 | ||
| <2 | 43 (7.5) | 207 (31.4) | |
| 2–5 | 109 (25.7) | 164 (33.9) | |
| >5 | 237 (66.8) | 190 (34.7) | |
| Age at first sexual intercourse | 17.1 (3.1) | 18.2 (3.8) | <.001 |
| Dietary vitamin C, mean, mg/d | 89.1 (79.0) | 86.0 (71.1) | .54 |
| Dietary vitamin C | .608 | ||
| Low (<70.7 mg/d) | 204 (52.2) | 270 (50.8) | |
| High (≥70.7 mg/d) | 185 (47.8) | 291 (49.2) | |
| Supplemental vitamin C, mean, mg/d | 179.8 (284.3) | 214.5 (327.8) | .103 |
| Supplemental vitamin C | .003 | ||
| Low (<80 mg/d) | 203 (56.5) | 272 (46.5) | |
| High (≥80 mg/d) | 186 (43.5) | 289 (53.5) | |
| Overall vitamin C, mean, mg/d | 268.9 (298.8) | 300.5 (337.4) | .152 |
| Overall vitamin C | .160 | ||
| Low (<176.26 mg/d) | 198 (54.1) | 277 (49.2) | |
| High (≥176.26 mg/d) | 191 (46.0) | 284 (50.7) | |
| Vitamin D, mean, mg/d | 79.7 (31.2) | 83.3 (32.2) | .094 |
| FA, mean, µg/d | 666.1 (311.8) | 690.7 (302.7) | .238 |
| Vitamin B1, mean, µg/d | 11.7 (28.9) | 14.5 (28.7) | .147 |
| Vitamin B2, mean, µg/d | 8.8 (14.6) | 10.9 (16.7) | .058 |
| NIAC, mean, mg/d | 49.6 (42.6) | 50.1 (34.9) | .828 |
| Vitamin B6, mean, µg/d | 9.9 (17.2) | 11.3 (17.6) | .232 |
| Vitamin B12, mean, µg/d | 80.6 (268.5) | 94.7 (360.4) | .531 |
Statistically significant values were shown in bold.
FA = folic acid, NHANES = National Health and Nutrition Examination Survey, NIAC = nicotinic acid, PIR = poverty income ratio.
Derived from χ2-test for categorical variables, general linear models for continuous variables.
The associations between dietary or supplemental VitC and HPV infection are shown in Table 2. Overall, the intake of VitC was negatively associated with the risk of both HPV and high-risk HPV. The intake of supplemental VitC was negatively associated with the risk of both HPV (P < .05) and high-risk HPV (P < .05) infection. Specifically, for each additional 100 mg of VitC supplement consumed per day, the overall risk of HPV infection in US women decreased by 6% (adjusted odds ratio [AOR] = 0.94, 95% CI = 0.89–0.99), and the risk for high-risk HPV decreased by up to 26% (AOR = 0.74, 95% CI = 0.55–0.99). Moderate dietary VitC intake was associated with a reduced risk of high-risk HPV infection (P = .049). A greater level of dietary VitC intake also had a potential protective effect on high-risk HPV infection, but this effect was not significant (P = .369).
Table 2.
Weighted association between vitamin C from food/supplements and HPV infection in multiple regression, NHANES, 2007–2016.
| Variables | N | Model 1* | Model 2† | Model 3‡ | ||||
|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | P | AOR (95% CI) | P | AOR (95% CI) | P | |||
| HPV infection | Overall vitamin C, per 100 mg/d | 0.97 (0.93–1.01) | .154 | 0.95 (0.90–1.00) | .033 | 0.95 (0.90–1.00) | .044 | |
| Overall vitamin C | ||||||||
| Low (<176.26 mg/d) | 475 | 1.0 | 1.0 | 1.0 | ||||
| High (≥176.26 mg/d) | 475 | 0.83 (0.63–1.08) | .160 | 0.71 (0.52–0.96) | .026 | 0.71 (0.52–0.98) | .040 | |
| Dietary vitamin C, per 100 mg/d | 1.06 (0.88–1.26) | .544 | 1.12 (0.92–1.36) | .262 | 1.18 (0.96–1.45) | .125 | ||
| Dietary vitamin C | ||||||||
| Low (<70.7 mg/d) | 474 | 1.0 | 1.0 | 1.0 | ||||
| High (≥70.7 mg/d) | 476 | 0.95 (0.72–1.23) | .681 | 1.03 (0.76–1.39) | .872 | 1.05 (0.77–1.44) | .738 | |
| Supplemental vitamin C, per 100 mg/d | 0.96 (0.92–1.01) | .107 | 0.94 (0.89–0.99) | .014 | 0.94 (0.89–0.99) | .017 | ||
| Supplemental vitamin C | ||||||||
| Low (<80 mg/d) | 475 | 1.0 | 1.0 | 1.0 | ||||
| High (≥80 mg/d) | 475 | 0.67 (0.51–0.87) | .003 | 0.56 (0.41–0.75) | <.001 | 0.53 (0.37–0.74) | <.001 | |
| High-risk HPV infection | Overall vitamin C, per 100 mg/d | 0.81 (0.67–0.98) | .030 | 0.82 (0.67–0.99) | .041 | 0.81 (0.66–0.99) | .043 | |
| Overall vitamin C | ||||||||
| Low (<176.26 mg/d) | 475 | 1.0 | 1.0 | 1.0 | ||||
| High (≥176.26 mg/d) | 475 | 0.66 (0.37–1.19) | .169 | 0.63 (0.34–1.18) | .152 | 0.62 (0.31–1.22) | .163 | |
| Dietary vitamin C, per 100 mg/d | 0.97 (0.65–1.45) | .893 | 1.02 (0.68–1.55) | .911 | 1.10 (0.72–1.70) | .656 | ||
| Dietary vitamin C | ||||||||
| Low (<44.7 mg/d) | 316 | 1.0 | 1.0 | 1.0 | ||||
| Middle (44.7–102.1 mg/d) | 317 | 0.44 (0.21–0.92) | .029 | 0.43 (0.20–0.94) | .033 | 0.46 (0.21–1.00) | .049 | |
| High (>102.1 mg/d) | 316 | 0.62 (0.32–1.23) | .174 | 0.64 (0.31–1.32) | .228 | 0.71 (0.33–1.50) | .369 | |
| Supplemental vitamin C, per 100 mg/d | 0.75 (0.58–0.98) | .035 | 0.75 (0.57–0.99) | .049 | 0.74 (0.55–0.99) | .044 | ||
| Supplemental vitamin C | ||||||||
| Low (<80 mg/d) | 475 | 1.0 | 1.0 | 1.0 | ||||
| High (≥80 mg/d) | 475 | 0.71 (0.39–1.27) | .244 | 0.69 (0.37–1.28) | .237 | 0.66 (0.33–1.32) | .237 | |
Statistically significant values were shown in bold.
AOR = adjusted odds ratio, CI = confidence interval, FA = folic acid, NHANES = National Health and Nutrition Examination Survey, NIAC = nicotinic acid, OR = odds ratio, PIR = poverty income ratio.
Model 1: univariable analysis.
Model 2: adjusted for age, race, education, PIR, vaccine, smoke, age at first sexual intercourse, and sex partners.
Model 3: adjusted for age, race, education, PIR, vaccine, smoke, age at first sexual intercourse, sex partners, vitamin D, FA, vitamin B1, nicotinic acid, vitamin B2, vitamin B6, and vitamin B12.
Our analysis revealed that only the relationship between dietary VitC intake and high-risk HPV infection was nonlinear and took an L-shape (Fig. 2 and Table 3) after multivariable adjustment using a smooth spline curve. The inflection point was determined to be 12.87 using 2-piecewise binary logistic regression and a recursive algorithm. The effect values were 1.31 (95% CI = 0.92–1.85) on the left and 1.00 (95% CI = 1.00–1.00) on the right side of the inflection point.
Figure 2.
Nonlinear relationshipa between vitamin C and HPV infection. (A) Nonlinear relationship between vitamin C from food and HPV infection. (B) Nonlinear relationship between vitamin C from food and high-risk HPV infection. (C) Nonlinear relationship between vitamin C from supplements and HPV infection. (D) Nonlinear relationship between vitamin C from supplements and high-risk HPV infection. (E) Nonlinear relationship between vitamin C from food and HPV infection after propensity score matchingb. (F) Nonlinear relationship between vitamin C from supplements and HPV infection after propensity score matchingb. aAdjusted for age, race, education, poverty income ratio, vaccine, smoking status, age at first sexual intercourse, sexual partners, vitamin D, folic acid, nicotinic acid, vitamin B1, vitamin B2, vitamin B6, and vitamin B12. bAdjusted for age, race, education, poverty income ratio, vaccine, smoking status, age at first sexual intercourse, sexual partners, vitamin D, folic acid, nicotinic acid, vitamin B1, vitamin B2, vitamin B6, and vitamin B12.
Table 3.
Weighted results of 2-piecewise linear model, NHANES 2007–2016.
| Outcome | HPV infection | P * | High-risk HPV infection | P * | |
|---|---|---|---|---|---|
| Overall vitamin C | Fitting model by 2-piecewise linear regression | ||||
| Inflection point of vitamin C, mg/d | 96.96 | 242.99 | |||
| <Inflection point | 1.00 (0.99–1.02) | .757 | 1.00 (0.99–1.00) | .695 | |
| >Inflection point | 1.00 (1.00–1.00) | .031 | 1.00 (0.99–1.00) | .108 | |
| Likelihood ratio test | .409 | .283 | |||
| Dietary vitamin C | Fitting model by 2-piecewise linear regression | ||||
| Inflection point of vitamin C, mg/d | 11.38 | 12.87 | |||
| <Inflection point | 0.95 (0.85–1.07) | .414 | 1.31 (0.92–1.85) | .129 | |
| >Inflection point | 1.00 (1.00–1.00) | .094 | 1.00 (1.00–1.00) | .925 | |
| Likelihood ratio test | .384 | .026 | |||
| Supplemental vitamin C | Fitting model by 2-piecewise linear regression | ||||
| Inflection point of vitamin C, mg/d | 251.8 | 180 | |||
| <Inflection point | 1.00 (0.99–1.00) | .016 | 1.00 (0.99–1.01) | .769 | |
| >Inflection point | 1.00 (1.00–1.00) | .838 | 0.99 (0.99–1.00) | .10 | |
| Likelihood ratio test | .19 | .058 | |||
Statistically significant values were shown in bold.
FA = folic acid, NHANES = National Health and Nutrition Examination Survey, NIAC = nicotinic acid, PIR = poverty income ratio.
Adjusted for age, race, education, PIR, vaccine, smoke, age at first sexual intercourse, sex partners, vitamin D, FA, NIAC, vitamin B1, vitamin B2, vitamin B6, and vitamin B12.
The relationship between VitC supplementation and HPV infection according to age and vaccination status are presented in Tables 4 and 5. Supplemental VitC intake was negatively associated with HPV infection in women ≥25 years of age (AOR = 0.52, 95% CI = 0.38–0.72); however, in women younger than 25, HPV infection was not related to the levels of supplemental VitC. Supplemental VitC intake also had a stronger protective effect on the unvaccinated population (Pinteraction = .03). For each additional 100 mg of supplementary VitC consumed per day, the risk of HPV infection in U.S. women decreased by 24% (AOR = 0.76, 95% CI = 0.59–0.98) in the unvaccinated population. In the vaccinated population, the protective effect was not significant when supplemental VitC intake was included as a continuous variable, but it was significant when supplemental VitC intake was included as a dichotomous variable. There was a significant interaction effect of vaccine status with supplemental VitC intake and HPV infection (Pinteraction = .02), indicating that supplemental VitC was more protective in the unvaccinated population.
Table 4.
Association between vitamin C from food/supplements and HPV infection in multiplicative regression for different age groups, NHANES 2007–2016.
| Variables | N | Model 1* | Model 2† | |||||
|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | P | P interaction | AOR (95% CI) | P | P interaction | |||
| Overall vitamin C, per 100 mg/d | 18–24 yr | 89 | 0.86 (0.72–1.02) | .090 | .093 | 0.84 (0.69–1.03) | .092 | .131 |
| 25–58 yr | 861 | 1.00 (0.96–1.04) | .903 | 0.98 (0.94–1.03) | .482 | |||
| Overall vitamin C | .430 | .146 | ||||||
| Low (<176.26 mg/d) | 18–24 yr | 44 | 1.0 | 1.0 | ||||
| High (≥176.26 mg/d) | 18–24 yr | 45 | 0.49 (0.18–1.35) | .168 | 0.35 (0.09–1.42) | .143 | ||
| Low (<176.26 mg/d) | 25–58 yr | 431 | 1.0 | 1.0 | ||||
| High (≥176.26 mg/d) | 25–58 yr | 430 | 0.85 (0.64–1.12) | .247 | 0.71 (0.51–0.97) | .031 | ||
| Dietary vitamin C, per 100 mg/d | 18–24 yr | 89 | 0.86 (0.46–1.59) | .621 | .62 | 0.86 (0.38–1.94) | .707 | .70 |
| 25–58 yr | 861 | 1.00 (0.96–1.04) | .903 | 0.98 (0.94–1.03) | .482 | |||
| Dietary vitamin C | .346 | .447 | ||||||
| Low (<70.7 mg/d) | 18–24 yr | 43 | 1.0 | 1.0 | ||||
| High (≥70.7 mg/d) | 18–24 yr | 46 | 0.61 (0.22–1.64) | .323 | 0.27 (0.05–1.39) | .119 | ||
| Low (<70.7 mg/d) | 25–58 yr | 432 | 1.0 | 1.0 | ||||
| High (≥70.7 mg/d) | 25–58 yr | 429 | 1.00 (0.75–1.32) | .978 | 1.05 (0.77–1.45) | .749 | ||
| Supplemental vitamin C, per 100 mg/d | 18–24 yr | 89 | 0.78 (0.61–1.00) | .052 | .06 | 0.69 (0.46–1.03) | .070 | .07 |
| 25–58 yr | 861 | 0.97 (0.93–1.02) | .261 | 0.95 (0.90–1.00) | .030 | |||
| Supplemental vitamin C | .635 | .104 | ||||||
| Low (<80 mg/d) | 18–24 yr | 43 | 1.0 | 1.0 | ||||
| High (≥80 mg/d) | 18–24 yr | 46 | 0.82 (0.30–2.21) | .689 | 0.76 (0.18–3.27) | .710 | ||
| Low (<80 mg/d) | 25–58 yr | 432 | 1.0 | 1.0 | ||||
| High (≥80 mg/d) | 25–58 yr | 429 | 0.64 (0.48–0.84) | .002 | 0.52 (0.38–0.72) | <.001 | ||
Statistically significant values were shown in bold.
AOR = adjusted odds ratio, CI = confidence interval, NHANES = National Health and Nutrition Examination Survey, OR = odds ratio, PIR = poverty income ratio.
Model 1: univariable analysis.
Model 2: adjusted for race, education, PIR, vaccine, smoke, age at first sexual intercourse, and sex partners.
Table 5.
Association between vitamin C from food/supplements and HPV infection according to vaccination status, NHANES 2007–2016.
| Variables | N | Model 1* | Model 2† | |||||
|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | P | P interaction | AOR (95% CI) | P | P interaction | |||
| Overall vitamin C, per 100 mg/d | No vaccination | 74 | 0.81 (0.68–0.97) | .02 | .01 | 0.81 (0.68–0.97) | .02 | .01 |
| Vaccination | 876 | 1.00 (0.96–1.05) | .915 | 1.00 (0.96–1.05) | .915 | |||
| Overall vitamin C | .433 | .839 | ||||||
| Low (<176.26 mg/d) | No vaccination | 33 | 1.0 | 1.0 | ||||
| High (≥176.26 mg/d) | No vaccination | 41 | 0.21 (0.07–0.61) | .004 | 0.32 (0.06–1.70) | .180 | ||
| Low (<176.26 mg/d) | Vaccination | 442 | 1.0 | 1.0 | ||||
| High (≥176.26 mg/d) | Vaccination | 434 | 0.89 (0.67–1.18) | .422 | 0.80 (0.58–1.09) | .155 | ||
| Dietary vitamin C, per 100 mg/d | No vaccination | 74 | 0.62 (0.32–1.20) | .157 | .48 | 0.78 (0.24–2.57) | .680 | .18 |
| Vaccination | 876 | 1.11 (0.92–1.34) | .272 | 1.16 (0.95–1.43) | .153 | |||
| Dietary vitamin C | .417 | .441 | ||||||
| Low (<70.7 mg/d) | No vaccination | 37 | 1.0 | 1.0 | ||||
| High (≥70.7 mg/d) | No vaccination | 37 | 0.66 (0.25–1.76) | .407 | 1.68 (0.31–9.24) | .551 | ||
| Low (<70.7 mg/d) | Vaccination | 438 | 1.0 | 1.0 | ||||
| High (≥70.7 mg/d) | Vaccination | 438 | 1.01 (0.76–1.34) | .955 | 1.07 (0.78–1.47) | .678 | ||
| Supplemental vitamin C, per 100 mg/d | No vaccination | 74 | 0.80 (0.68–0.95) | .008 | .02 | 0.76 (0.59–0.98) | .034 | .03 |
| Vaccination | 876 | 0.98 (0.93–1.02) | .326 | 0.96 (0.91–1.01) | .103 | |||
| Supplemental vitamin C | .202 | .553 | ||||||
| Low (<80 mg/d) | No vaccination | 35 | 1.0 | 1.0 | ||||
| High (≥80 mg/d) | No vaccination | 39 | 0.34 (0.12–0.95) | .039 | 0.46 (0.89–2.41) | .360 | ||
| Low (<80 mg/d) | Vaccination | 439 | 1.0 | 1.0 | ||||
| High (≥80 mg/d) | Vaccination | 437 | 0.68 (0.51–0.90) | .007 | 0.58 (0.42–0.80) | <.001 | ||
Statistically significant values were shown in bold.
AOR = adjusted odds ratio, CI = confidence interval, NHANES = National Health and Nutrition Examination Survey, OR = odds ratio, PIR = poverty income ratio.
Model 1: univariable analysis.
Model 2: adjusted for age, race, education, PIR, vaccine, smoke, age at first sexual intercourse, and sex partners.
4. Discussion
In this study, we found that overall VitC intake and supplementation with VitC were significantly and negatively associated with both HPV infection and high-risk HPV infection. Dietary VitC intake also had a potential inverse association with high-risk HPV infection. The supplemental VitC intake was negatively associated with all HPV infections in women older than 25 years of age and was with a stronger negative association in those who did not receive HPV vaccination.
We found a negative association between dietary VitC intake and HPV infection. Barchitta et al reported a lower intake of VitC in HPV-positive women.[12] Another study reported that dietary intake of VitC was inversely related to the risk of HPV persistence in a case-control study.[11] Therefore, VitC intake may help prevent HPV infection and contribute to the prevention of cervical cancer. Another study revealed that the concentration of VitC may be substantially lower in patients with cervical cancer than in healthy individuals.[20] We had the same trends as previous studies, and the 95% CI also overlaps with those of these studies for overall VitC. We further reported that the protective effect against HPV, especially against high-risk HPV, was driven mainly by supplemental VitC, which further suggests that VitC intake may contribute to the prevention cervical cancer.
We found that this negative association was observed only for supplemental VitC intake but not for dietary VitC intake. We observed a nonlinear L-shaped association between dietary VitC and HPV infection. The overall nonsignificant association between dietary VitC and HPV infection might be due to this nonlinearity in that the low-dose and medium-dose, but not high-dose, dietary VitC intake, which were significantly associated with lower rates of HPV infection. For supplemental VitC intake, we found a negative, linear, dose-response relationship with HPV infection. For the first time, we observed this linear and nonlinear difference in the associations of dietary and supplemental VitC intake with HPV infection. Previous studies did not address the effects of dietary and supplemental VitC separately[11–14] and were not conducted in normal populations[11–13] or focused on the associations between serum VitC concentrations[13,14] and HPV infection. This different relationship between dietary and supplemental VitC intake and HPV infection is intriguing and worthy of further exploration.
The negative association between VitC and HPV infection was observed only in women aged ≥25 years but not in women <25 years in our study, which is consistent with the results of a recent study.[14] This could relate to the high prevalence of HPV infection in women <25 years and the high rate of natural clearance following HPV infection.[14] Furthermore, older women benefit less from cervical cancer vaccination.[21] The interaction effect between supplemental VitC and HPV infection was significant for different HPV vaccination statuses. HPV vaccination is a strong protection factor for reducing HPV infection; therefore, the weaker effect of VitC intake may be masked. Therefore, for patients who have not received the vaccine, the protective effect of VitC supplementation on HPV infection is clearly demonstrated. However, the effect of VitC intake on HPV infection may also be due to various confounding factors. People with higher overall VitC or supplemented VitC intake may have healthier lifestyles and better health conditions.[22]
Mechanistically, VitC intake may help prevent HPV infection, contributing to reducing the incidence of HPV-related cancers. The reactive oxygen species (ROS), highly reactive compounds, can lead to cellular damage, disregulate cell signaling, and increase viral replication and viral expression.[23] VitC can ROS, which are mainly released by the activation of phagocytes during infection, preventing viral infection and protecting the host from infection.[24] Antioxidants have been found to suppress the activation of AP-1, a key transcription factor for expressing oncoproteins E6 and E7 in oncogenic HPVs,[25,26] according to in vitro studies. VitC also potentiates host cellular and humoral immunity.[25] And its cofactor activity for Fe- or Cu-containing oxygenases is emerging as a key factor in the functional effects on both the innate and adaptive immune responses,[27,28] which is important in the defense of HPV infection. VitC from supplements is absorbed more rapidly than VitC from food,[29] creating a higher serum VitC concentration more quickly, particularly in cases of inflammation where VitC often becomes deficient.[30] Therefore, supplemental VitC may better quench ROS.[29]
The greater actual absorption of VitC from supplements, as opposed to food, can be attributed to the protective coating commonly found in supplement formulations. Dietary VitC is subject to degradation during washing, cooking,[31,32] and exposure to the alkaline gut environment. Furthermore, the rapid absorption of supplemental VitC leads to prompt elevations in plasma concentrations. This increased plasma level facilitates greater storage within white blood cells, where VitC accumulates after plasma saturation,[33] providing a more potent anti-infective effect.
Our study has several advantages. First, our sample size was comparatively larger than that of previous studies. The large sample sizes enabled us to conduct stratified analyses and address the different effects of dietary and supplemental VitC intake on HPV infection. Second, our findings are robust, as demonstrated by the consistent results from various sensitivity analyses we performed. This study has several limitations. First, current methods for detecting HPV DNA detection in large epidemiological research cannot identify if it is an active infection or figure out whether HPV comes from the participant or their partner.[34] Second, as the research was restricted to a group of 950 women from 18 to 59 years from America, the findings may not be readily generalizable to other women. Third, due to the cross-sectional nature of the study, the inability to prove causality was preserved.
In this study, we found that overall VitC intake and supplementation with VitC were significantly and negatively associated with a high risk of HPV infection. In addition, we found a linear relationship between supplementary VitC and HPV infection and an L-shaped relationship between dietary VitC intake and HPV infection. Our results support that the protective effect of VitC against HPV infection was driven mainly by supplemental VitC rather than dietary VitC, which may potentially reduce the incidence of cervical cancer. Our study also suggested that women, especially those older than 26 years, who did not receive HPV vaccination might also reduce HPV infection via the intake of VitC, especially supplements. Although this was a cross-sectional study, our findings warrant further exploration and verification in well-designed prospective studies to further reduce the disease burden of HPV infection and related cancers.
Acknowledgments
We sincerely thank the U.S. National Health and Nutrition Examination Survey staff for providing this invaluable database.
Author contributions
Conceptualization: Zheyu Huang, Zhenming Fu.
Data curation: Zheyu Huang, Yuxuan Wei.
Formal analysis: Yuxuan Wei, Jianglong Han, Tingting Jian.
Investigation: Jianglong Han, Ruyan Chen.
Methodology: Ruyan Chen, Haiyu Deng.
Project administration: Haiyu Deng.
Software: Tingting Jian.
Validation: Si Li.
Visualization: Si Li.
Writing – original draft: Zheyu Huang, Zhenming Fu.
Writing – review & editing: Zhenming Fu.
Abbreviations:
- AOR
- adjusted odds ratio
- CI
- confidence interval
- HPV
- human papillomavirus
- NHANES
- National Health and Nutrition Examination Survey
- PIR
- poverty income ratio
- VitC
- vitamin C
The authors have no funding and conflicts of interest to disclose.
Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.
How to cite this article: Huang Z, Wei Y, Han J, Chen R, Deng H, Jian T, Li S, Fu Z. Different associations between dietary or supplemental vitamin C intake and HPV infection in American women: A cross-sectional study. Medicine 2025;104:27(e43015).
Contributor Information
Zheyu Huang, Email: 2019305231098@whu.edu.cn.
Yuxuan Wei, Email: 2019305231080@whu.edu.cn.
Jianglong Han, Email: 2014302180198@whu.edu.cn.
Ruyan Chen, Email: ruyanchen@whu.edu.cn.
Haiyu Deng, Email: haiyudeng349@whu.edu.cn.
Tingting Jian, Email: 2017302180033@whu.edu.cn.
Si Li, Email: 2018305231011@whu.edu.cn.
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